GB2035517A

GB2035517A - Hydraulic system with unloading valve

Info

Publication number: GB2035517A
Application number: GB7936418A
Authority: GB
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1978-10-23
Filing date: 1979-10-19
Publication date: 1980-06-18
Also published as: US4209984A; IT7950633A0; GB2035517B; DE2942650C2; IT1203252B; YU257079A; FR2439893B1; AR225155A1; FR2439893A1; DE2942650A1; CA1107174A; AU5092579A; AU525749B2; JPS5557704A; ES485248A1

Description

1 GB2035517A 1

SPECIFICATION

Hydraulic system with unloading valve This invention relates to a hydraulic system 70 employing a charge pump and a supply pump.

In the past, a direction control valve has been used to automatically direct the return fluid of a single acting device to the fluid reservoir and to direct the return fluid of continuously acting and/or double acting de vices to a charging circuit for the supply pump, as described in our U.S. Patent Speci- fication 3,973,398.

An accepted disadvantage of the prior art is that the return fluid of continuously acting and/or double acting devices must be at the maximum charge circuit pressure during oper ation of any of these devices so that the 85 return fluid can provide the bulk of the fluid feeding the supply pump. Since the usable pressure for a device is the difference between its supply and return pressures, it is evident that a power penalty exists because of the difference between reservoir and return pres sures. Where it has been desired to increase the power output of a device without increas ing the size of the device itself, the practice has been to increase the supply pressure by providing a larger pump with the acceptance of this power penalty.

According to the present invention, there is provided a hydraulic system comprising a charge pump drawing fluid from a reservoir and feeding a supply pump by way of a charge passage, the supply pump being con nected by way of a supply passage and one or more control valves to one or more actuated devices which connect back to a return pas sage, the charge and return passages being connected to a main passage in the valve body of an unloading valve which further comprises a spool in a bore intersecting both the main passage and a reservoir passage which communicates with the reservoir, the spool being acted upon at one end by the pressure in a control passage and at the other end by biasing means and being responsive to increasing pressure in the control passage to move from a position in which communication between the main passage and the reservoir passage is blocked to progressively open com munication between these passages, the con trol passage being connected to the charge passage and through a restricted flow orifice in the valve body to the reservoir passage.

In operation, the unloading valve routes all flow from the single acting, double acting, and/or continuously acting devices as well as from the charge pump directly to the reservoir when the pressure at the inlet of the supply pump is above a predetermined level. As the pressure drops because of usage at the vari ous devices, the pressure drops, causing the valve to route more fluid from the charge and the return passages to the supply pump to return the pressure to the predetermined level. As all devices begin to operate, the valve will operate to clock the charge and return passages from the reservoir.

In the preferred embodiment, the charge passage is nearer to the said one end of the spool than is the reservoir passage.

The unloading valve can include a second spool which is responsive to the pressure differential across the filter to provide a signal indicative of the clogging of the filter. The signal valve further operates to connect the charge pump directly to the reservoir when the filter is clogged.

The invention will provide cold weather protection by providing for continuous circulation of return fluid whenever the charge pump has difficulty in providing enough pressurized fluid for the supply pump. The invention will also lead to lower standby losses because lower system pressures can be used to provide the same power output.

The drawing is a schematic illustration partially in section of a hydraulic system embodying the present invention, which will now be described by way of example.

A hydraulic system 10 includes a fluid reservoir 12 containing fluid to be drawn through a charge pump filter 14 by a charge pump 16. The charge pump 16 is connected to a charge passage 18 which has disposed therein a main filter 20. The charge passage 18 is further connected to a supply pump 22 which is addition to internally carrying the charge passage 18 supplies high pressure fluid to a supply passage 24.

The supply passage 24 is connected to a series of direction control valves 26, 28, and 30 which in the illustrated embodiment are respectively connected to a reversible hydraulic motor 32, a single acting cylinder 34, and a double acting cylinder 36. The direction control valves 26, 28, and 30 are further connected to a return passage 38.

The return passage 38 8s connected to an unloading valve assembly 40 which is connected to the charge passage 18 in parallel with the main filter 20 and which is further connected to the reservoir passage 39.

The unloading valve assembly 40 includes a valve body 42 having an unloading valve bore 44 which is plugged at one end by a plug 46 against which is seated a spring 48. The spring 48 biases an unloading valve spool 50 against the far end of the unloading valve bore 44, i.e. the right end in the draw- ing of the unloading valve bore 44.

The unloading valve spool 50, starting from the right has first and second lands 52 and 54 separated by a groove 58. A passage 62 through the unloading valve spool 50 con- nects the left or spring side of the unloading 12 by a reservoir 2 GB2035517A 2 valve spoof 50 to a reservoir passageway 64 which is connected to the reservoir passage 39. Parallel to and adjacent the reservoir passageway 64 is a main passageway 66 which connects the unloading valve bore 44 to the charge passage 18. A return passageway 68, connected to the return passage 38, intersects the main passageway 66 between the charge passage 18 and the unloading valve bore 44.

The right end of the unloading valve bore 44 is connected to a check valve passageway 82 which is connected to a check valve 84. The check valve 84 contains a conventional retainer 86, a spring 88, and a ball 90 to allow flow from the charge passage 18 to the check valve passageway 82 and prevent flow in the reverse direction. The check valve 84 thus eliminates the possibility of unfiftered fluid being drawn into the supply pump 22.

The check valve passageway 82 is connected to first and second passageways 92 and 94 which are spaced apart and connected to a signal valve bore 96 provided in the valve body 42. The signal valve bore 96 is plugged at the left end by a plug 98 which includes a sealed signal plunger 100. Abutting the plug 98 is a spring 102 which abuts a head on the end of a spacer pin 104. The spacer pin 104 further abuts a spring 106 which biases a signal valve spool 108 against the right end of the signal valve bore 96. The right end of the signal valve bore 96 is further connected by a signal passageway 110 to the unloading valve bore 44 and thence to the main charge passageway 66.

The first and second passageways 92 and 94 and the check valve passageway 82 are commonly connected by an orifice 112 to the reservoir passageway 64.

During operation of the hydraulic system 10, when all the direction control valves 26, 28, and 30 are in the closed position shown, the charge pump 16 will provide pressurized fluid to the charge passage 18 which will be at a predetermined standby pressure level maintained by the restriction of flow through the check valve 84 and the orifice 112. The pressure in the charge passage 18 at the inlet of the supply pump 18 is transmitted through the check valve 84 and the check valve passageway 82 to impart a pressure to the right hand end of the unloading valve bore 44 which shifts the unloading valve spool 50 to its extreme left hand position so as to compress the spring 48.

With the unloading valve spool 50 in its left hand position, the main passageway 66 and thus the charge and return passages 18 and 38 are connected to the reservoir passageway 64 by the grooves 58. In this position, the low pressure return fluid from the direction control valves is connected directly to the reservoir 12 and only that fluid from the charge pump 16 necessary to maintain the standby pressure required at the supply pump 22 is provided thereto, the remainder being diverted through the main passageway 66 back to the reservoir 12.

As one of the actuated devices starts to draw fluid from the supply pump 22, for example, the reversible hydraulic motor 32, the pressure of pressurized fluid at the inlet of the supply pump 22 will be slightly reduced.

This reduction below the predetermined standby pressure level causes a reduction in the pressure in the check valve passageway 82 and causes movement of the unloading valve spool 50 to the right. This movement causes a metering of fluid from the main passageway 66 across the land 54 of the unloading valve spool 50 and causes a corresponding increase in the pressure in the charge passageway 18 to counteract the re- duction caused by the draw from the supply pump 22. At this point, all of the return fluid and most of the charge fluid will be flowing to the reservoir 12.

As more fluid is required from the supply pump 22, for example if the double acting cylinder 36 as well as the reversible hydraulic motor 32 is in operation, the pressure of fluid at the inlet of the supply pump 22 will tend to be further reduced, causing the pressure in the right hand end of the unloading valve bore 44 to decrease to the point where the land 54 of the unloading valve spool 50 will cause the full output of the charge pump 16 to be fed to the charge passage 18.

As the full output of the supply pump 22 is required with all devices in operation, i.e. when both the single and double acting cylinders 34 and 36 are well as the reversible hydraulic motor 32 are in operation, the pressure of pressurized fluid in the charge passage 18 will be reduced past a predetermined minimum pressure level. This causes the unloading valve spool 50 to move to completely to the right, causing the land 54 to block the main passageway 66 from the reservoir passageway 64. As a result of this blockage, pressure in the return passageway 38 will increase with both the charge and return passages 18 and 38 supplying pressurized fluid to the supply pump 22. As the various functions are shut down, the sequence of operation will reverse, so that at the standby pressure level, the return fluid from the direction control valves and the charge fluid will again be connected to the reservoir 12.

One additional advantage of this system, is that fluid for the most part is returned to the reservoir 12 because it is drawn up by the charge pump 16 through the charge pump filter 14 and dumped to reservoir 12 when the supply pump 22 has no demand. This prolongs the filter life of the main filter 20 and provides a cleaner system.

The unloading valve assembly 40 is con- nected across the main filter 20 so as to be 3 GB 2 035 517A 3 capable of providing a visual indication of when the main filter 20 is clogged as well as preventing operation of the actuated devices when the filter is clogged. As the main filter 20 clogs, the pressure on the charge pump side increases, causing the pressure in the main and signal passageways 66 and 110 to increase. At a predetermined pressure difference across the main filter 20 as sensed by the pressure in the signal passageway 110 being greater than that sensed through the first passageway 92 plus the force of the springs 102 and 106, the signal valve spool 108 moves to the left, causing the spacer pin 104 to press the signal plunger 100 to the left causing the stem of the signal plunger 100 to protrude, thereby indicating that the filter is clogging. With a further increase in the pressure in the signal passageway 110, the signal valve spool 108 opens. The pressurized fluid from the signal passageway 110 is then transmitted through the first and second passageways 92 and 94 to the check valve passageway 82 causing (1) the check valve 84 to close thus preventing dirty oil from reaching the supply pump 22 and (2) the unloading valve spoof 50 to move to the left to the position in which the main passageway 66 is connected to the reservoir passa- geway 64 by the groove 54. After the main filter 20 is cleaned, the unloading valve assembly 40 automatically resets itself for normal operation.

In a modification, the spool controls the connection of the charge line 18 and return line 38 individually so that, as the spool moves to the left, firstly only the return line is progressively vented to the reservoir, whereafter the charge line is also progressively vented.

Claims

1. A hydraulic system comprising a charge pump drawing fluid from a reservoir and feed- ing a supply pump by way of a charge 110 passage, the supply pump being connected by way of a supply passage and one or more control valves to one or more actuated devices which connect back to a return passage, the charge and return passages being connected to a main passage in the valve body of an unloading valve which further comprises a spool in a bore intersecting both the main passage and a reservoir passage which com- municates with the reservoir, the spool being acted upon at one end by the pressure in a control passage and at the other end by biasing means and being responsive to increasing pressure in the control passage to move from a position in which communication between the main passage and the reservoir passage is blocked to progressively open communication between these passages, the control passage being connected to the charge passage and through a restricted flow orifice in the valve body to the reservoir passage.

2. A hydraulic system according to claim 1, wherein the main passage is nearer to the said one end of the spool than is the reservoir passage.

3. A hydraulic system according to claim 1 or 2, wherein the control passage includes a check valve preventing fluid return from the unloading valve to the charge passage.

4. A hydraulic system according to claim 1, 2 or 3, wherein the charge passage is connected to the main passage upstream of a filter in the charge passage and is connected to the control passage downstream of the filter.

5. A hydraulic system according to any of claims 1 to 4, comprising a second valve spool acted upon at one end by the pressure in the main passage and at the other end by the pressure in the control passage and movable when the former pressure exceeds the latter by a predetermined amount to connect the main passage to the control passage and thereby cause the first said spool to move to put the main passage in communication with the reservoir pass.

6. A hydraulic system according to claim 5, comprising a signal device actuated by movement of the second spool to signal an excess pressure differential between the main and control passages.

7. A hydraulic system according to claim 6, wherein the signal device provides a signal in response to a smaller movement of the second spool than is required to connect the main passage to the control passage.

8. A hydraulic system according to any of claims 1 to 7, modified in that the movement of the first said spool from the said position firstly progressively vents only the return passage to the reservoir and then progressively vents also the charge passage to the reservoir.

9. A hydraulic system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd-1 980. Published at The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.